mm/page-writeback.c: improve arithmetic divisions

Use div64_ul() instead of do_div() if the divisor is unsigned long, to
avoid truncation to 32-bit on 64-bit platforms.

Link: http://lkml.kernel.org/r/20200102081442.8273-4-wenyang@linux.alibaba.com
Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Qian Cai <cai@lca.pw>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c74c6bd..2caf780 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1102,7 +1102,7 @@ static void wb_update_write_bandwidth(struct bdi_writeback *wb,
        bw = written - min(written, wb->written_stamp);
        bw *= HZ;
        if (unlikely(elapsed > period)) {
-               do_div(bw, elapsed);
+               bw = div64_ul(bw, elapsed);
                avg = bw;
                goto out;
        }